JP2018205660A - Fixing device and image forming apparatus - Google Patents

Abstract

Provided is a fixing device that can prevent a temperature drop at a longitudinal end portion of a fixing member and prevent damage due to sliding with a member forming a fixing nip portion with time, and has a long life and high energy savings. To do. A rotatable endless fixing member, a heating source for heating the fixing member, a nip forming unit disposed inside the fixing member, and the nip forming unit via the fixing member. The nip forming unit is in contact with the inner peripheral surface of the fixing member 21, the thickness does not change due to the pressing of the counter rotator 22, and the heat transfer is performed. The fixing device is provided with at least a nip member 27 for performing the above operation, and the counter rotating body 22 is shorter in the longitudinal direction than the nip member 27 and is disposed in a region facing the nip member 27. [Selection] Figure 9

Description

  The present invention relates to a fixing device and an image forming apparatus including the fixing device.

In recent years, market demands for energy saving and high speed have been increasing for image forming apparatuses such as printers, copiers, and facsimiles.
In an image forming apparatus, an unfixed toner image is transferred to a recording material sheet, printing paper, photosensitive paper, electrostatic recording paper, etc. by an image transfer method or a direct method by an image forming process such as electrophotographic recording, electrostatic recording, or magnetic recording. Formed on recording material. As a fixing device for fixing an unfixed toner image, a contact heating method fixing device such as a heat roller method, a film heating method, and an electromagnetic induction heating method is widely used.

  As an example of such a fixing device, a belt-type fixing device (for example, see Patent Document 1) and a surf fixing (film fixing) fixing device using a ceramic heater (for example, see Patent Document 2) are known. .

  In recent years, with belt type fixing devices, further warm-up time (time required from room temperature to a predetermined printable temperature (reload temperature) such as when the power is turned on) and first print time (after receiving a print request, It is desired to shorten the time required for the printing operation to be completed after the printing preparation is completed (first problem).

  In addition, as the speed of image forming apparatuses increases, the number of sheets to be passed per unit time increases and the required amount of heat increases, so that there is a problem that the amount of heat is insufficient (so-called temperature drop), particularly at the beginning of continuous printing. (Second problem).

  On the other hand, in the fixing device by surf fixing using a ceramic heater, the heat capacity can be reduced and the size can be reduced as compared with the belt type fixing device. However, since only the nip portion is locally heated, other portions are heated. However, the belt is in the coldest state at the entrance to the nip portion, and there is a problem that fixing failure is likely to occur. In particular, in a high-speed machine, there is a problem that fixing failure is more likely to occur because the belt rotates fast and the heat radiation of the belt outside the nip portion increases (third problem).

  In order to solve the above first to third problems, it is possible to warm the entire endless belt, shorten the first print time, and solve the shortage of heat during high-speed rotation, resulting in a high-production image forming apparatus There has been proposed a fixing device capable of obtaining good fixing properties even when mounted (see, for example, Patent Document 3).

In the fixing device of Patent Document 3, a pipe-shaped metal heat conductor is fixed inside the endless belt so as to be able to guide the movement of the endless belt, and the endless belt is moved through the metal heat conductor by a heat source in the metal heat conductor. Heated. Furthermore, a pressure roller that forms a nip portion in contact with the metal heat conductor via an endless belt is provided, and the endless belt is moved in the circumferential direction so as to rotate along with the rotation of the pressure roller (see Patent Document 3). (See FIG. 1).
With this configuration, the entire endless belt constituting the fixing device can be warmed, the first print time from the heating standby time can be shortened, and the lack of heat during high-speed rotation can be resolved. Yes.

  On the other hand, it is necessary to further improve the thermal efficiency in order to further save energy and improve the first print time. Then, the structure which heats an endless belt directly without passing through a metal heat conductor from the structure which heats an endless belt indirectly through a metal heat conductor is proposed (for example, refer patent document 4).

  Since the fixing device of Patent Document 4 is configured to directly heat the entire low heat capacity fixing belt and greatly improve the heat transfer efficiency, it further shortens the warm-up time and the first print time, and also reduces the amount of heat during continuous printing. Even if the shortage is solved and it is mounted on a high-production image forming apparatus, good fixability can be obtained. In addition, the cost can be reduced because there is no metal heat conductor.

  In the fixing device of Patent Document 4, a sliding sheet is disposed on at least the surface of the base pad that faces the fixing belt, thereby maintaining good slidability. By including a lubricant such as silicone oil in the sliding sheet, the sliding property can be further improved, and the durability of the fixing unit is further improved.

By the way, as in the fixing device of Patent Document 4, when the sliding sheet is disposed up to the vicinity of the end of the base pad, the lubricant moves to the end of the base pad due to the pressure of the pressure roller that forms the fixing nip. In some cases, there is a problem of leaking into the fixing unit.
In order to prevent this, it is conceivable that the range in which the sliding sheet 26 is disposed is set as an area inside the end of the base pad so as to return to the range of the fixing belt 121 even if the lubricant leaks. (See FIGS. 12A and 12B).
However, compared with the configuration in which the conventional sliding sheet 26 is disposed up to the end of the base pad (see FIGS. 13A and 13B), as shown in the broken circle in FIG. There is a problem that the end portion of the sheet 26 comes into contact with the inner periphery of the fixing belt 121 and the fixing belt 121 is easily damaged by rubbing. On the other hand, in the example of FIG. 13A, the sliding sheet 26 is disposed up to the vicinity of the end of the base pad (position overlapping the support member 44), and the end of the sliding sheet 26 contacts the inner periphery of the fixing belt 121. Not touching.

  Further, when the sliding sheet is made of a member in which a high heat-resistant thread is woven into a cloth shape, since the inside of the member includes a gap, the thickness is changed by being compressed by being pressed by a pressure roller. The end portion of the sliding sheet that is not pressed by the pressure roller is thicker than the pressed region, and easily comes into contact with the inner periphery of the fixing belt. That is, there is a problem that the inner periphery of the fixing belt is rubbed by the end portion of the sliding sheet and is easily damaged.

  On the other hand, there is also known a configuration in which a member (a nip plate formed of an aluminum plate or the like: see, for example, Patent Document 5) whose thickness is not changed by pressing of a pressure roller is applied as a nip member. However, since the thermal conductivity of such a nip member is large, by disposing the nip member up to the end of the fixing belt, the amount of heat to be transferred to the recording material in the fixing nip portion is different from that connected to the nip member. There is a problem that the energy is saved due to transmission to a member (for example, a flange or the like).

  Accordingly, the present invention can prevent a temperature drop at the longitudinal end portion of the fixing member and prevent damage due to sliding with a member forming the fixing nip portion over time, and has a long life and high energy saving. The purpose is to provide.

  In order to achieve such an object, a fixing device according to the present invention includes a rotatable endless fixing member, a heating source for heating the fixing member, a nip forming unit disposed inside the fixing member, A counter rotating body that forms a fixing nip portion with the nip forming unit via the fixing member, and the nip forming unit abuts against an inner peripheral surface of the fixing member and presses the counter rotating body. At least a nip member that performs heat transfer, and the counter rotating body is shorter in the longitudinal direction than the nip member, and is disposed in a region facing the nip member. The fixing device is characterized in that.

  According to the present invention, it is possible to prevent a temperature drop at the end portion in the longitudinal direction of the fixing member and to prevent damage with time due to rubbing with a member forming the fixing nip portion, and to achieve a long life and high energy saving fixing. An apparatus can be provided.

1 is a schematic diagram illustrating an image forming apparatus according to an embodiment of the present invention. FIG. 10 is a schematic cross-sectional configuration diagram illustrating an embodiment of a conventional fixing device. It is a perspective view which shows one Embodiment of the conventional fixing device. FIG. 4 is a diagram schematically showing a side surface of one end portion of the fixing device of FIG. 3. 1 is a schematic cross-sectional configuration diagram showing an embodiment of a fixing device of the present invention. (A) is a perspective view which shows the basic composition of the nip formation unit of the fixing device of this invention, (b) And (c) is a figure which shows the modification of a base member. FIG. 3 is a perspective view showing a basic configuration (when assembled) of a nip forming unit of the fixing device of the present invention. It is the figure which showed typically the state which the fixing belt inner peripheral surface contacted the nip member, (b) is an enlarged view of the one end part of (a). FIG. 6 is a diagram schematically illustrating a state in which the inner peripheral surface of the fixing belt is not in contact with the nip member, and (b) is an enlarged view of one end portion of (a). FIG. 3 is a diagram schematically illustrating a side surface of one end portion in the embodiment of the fixing device of the present invention. FIG. 3 is a diagram schematically illustrating a side surface of one end portion in the embodiment of the fixing device of the present invention. It is explanatory drawing which shows an example of the positional relationship of the edge part position of a sliding sheet | seat in a conventional fixing device, and a fixing member, (a) is a side surface schematic diagram, (b) is a perspective view. It is explanatory drawing which shows an example of the positional relationship of the edge part position of the sliding sheet | seat in a conventional fixing device, and a fixing member, (a) is a side surface schematic diagram, (b) is a perspective view.

  Hereinafter, a fixing device and an image forming apparatus according to the present invention will be described with reference to the drawings. The present invention is not limited to the embodiments described below, and other embodiments, additions, modifications, deletions, and the like can be changed within a range that can be conceived by those skilled in the art, and any aspect is possible. As long as the functions and effects of the present invention are exhibited, the scope of the present invention is included.

FIG. 1 is a schematic diagram showing an image forming apparatus according to an embodiment of the present invention.
The image forming apparatus 1 is a color laser printer. In the center of the printer body, four image forming units 4Y, 4C, 4M, and 4K are provided side by side along the extending direction of the intermediate transfer belt 30. Yes. Each of the image forming units 4Y, 4C, 4M, and 4K stores developers of different colors of yellow (Y), cyan (C), magenta (M), and black (K) corresponding to the color separation components of the color image. Other than that, the configuration is the same.

  Specifically, each of the image forming units 4Y, 4C, 4M, and 4K constituting the image station includes a drum-shaped photoconductor 5 as a latent image carrier, a charging device 6 that charges the surface of the photoconductor 5, and A developing device 7 for supplying toner to the surface of the photoreceptor 5 and a cleaning device 8 for cleaning the surface of the photoreceptor 5 are provided. In FIG. 1, only the photoconductor 5, the charging device 6, the developing device 7, and the cleaning device 8 included in the black image forming unit 4 </ b> K are assigned color codes, and the other image forming units 4 </ b> Y, 4 </ b> C, and 4 </ b> M The reference numerals are omitted.

Below the image forming units 4Y, 4C, 4M, and 4K, an exposure device 9 that exposes the surface of the photoreceptor 5 is disposed. The exposure device 9 includes a light source, a polygon mirror, an f-θ lens, a reflection mirror, and the like, and irradiates the surface of each photoconductor 5 with laser light based on image data.
A transfer device 3 is disposed above the image forming units 4Y, 4C, 4M, and 4K. The transfer device 3 includes an intermediate transfer belt 30 as a transfer body, four primary transfer rollers 31 as primary transfer means, and a secondary transfer roller 36 as secondary transfer means. Further, the transfer device 3 includes a secondary transfer backup roller 32, a cleaning backup roller 33, a tension roller 34, and a belt cleaning device 35.

  The intermediate transfer belt 30 is an endless belt and is stretched by a secondary transfer backup roller 32, a cleaning backup roller 33, and a tension roller 34. Here, when the secondary transfer backup roller 32 is driven to rotate, the intermediate transfer belt 30 runs (rotates) in the direction indicated by the arrow in the figure.

  Each of the four primary transfer rollers 31 sandwiches the intermediate transfer belt 30 with each photoconductor 5 to form a primary transfer nip. In addition, each primary transfer roller 31 is connected to a power source of a printer main body, and a predetermined DC voltage (DC) and / or AC voltage (AC) is applied to each primary transfer roller 31. .

  The secondary transfer roller 36 sandwiches the intermediate transfer belt 30 with the secondary transfer backup roller 32 to form a secondary transfer nip. Similarly to the primary transfer roller 31, the secondary transfer roller 36 is also connected to the power source of the printer main body, and a predetermined DC voltage (DC) and / or AC voltage (AC) is applied to the secondary transfer roller 36. It has come to be.

  The belt cleaning device 35 includes a cleaning brush and a cleaning blade disposed so as to contact the intermediate transfer belt 30.

  A bottle container 2 is provided in the upper part of the printer main body, and four toner bottles 2Y, 2C, 2M, and 2K containing replenishing toner are detachably attached to the bottle container 2. As is well known, a replenishment path is provided between each toner bottle 2Y, 2C, 2M, 2K and each developing device 7, and each development from each toner bottle 2Y, 2C, 2M, 2K is performed via this replenishment path. The toner is supplied to the device 7.

  On the other hand, a lower portion of the printer main body is provided with a paper feed tray 10 that stores paper P as a recording material, a paper feed roller 11 that carries the paper P out of the paper feed tray 10, and the like. Here, in addition to plain paper, the recording material includes thick paper, postcard, envelope, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, OHP sheet, and the like. Further, as is well known, a manual paper feed mechanism may be provided.

  In the printer main body, a transport path R is provided for discharging the paper P from the paper feed tray 10 through the secondary transfer nip to the outside of the apparatus. In the transport path R, a pair of registration rollers 12 serving as transport means for transporting the paper P to the secondary transfer nip is disposed upstream of the position of the secondary transfer roller 36 in the paper transport direction.

  Further, a fixing device 20 for fixing the unfixed image transferred onto the paper P is disposed downstream of the position of the secondary transfer roller 36 in the paper transport direction. Further, a pair of paper discharge rollers 13 for discharging the paper to the outside of the apparatus is provided downstream of the fixing device 20 in the paper conveyance direction of the conveyance path R. In addition, a paper discharge tray 14 for stocking paper discharged outside the apparatus is provided on the upper surface of the printer main body.

Next, the basic operation of the printer according to the present embodiment will be described with reference to FIG.
When the image forming operation is started, the photoconductors 5 in the image forming units 4Y, 4C, 4M, and 4K are rotationally driven clockwise in the drawing, and the surface of each photoconductor 5 is set to a predetermined polarity by the charging device 6. Uniformly charged. The surface of each charged photoconductor 5 is irradiated with laser light from the exposure device 9 to form an electrostatic latent image on the surface of each photoconductor 5. At this time, the image information to be exposed on each photoconductor 5 is single-color image information obtained by separating a desired full-color image into color information of yellow, cyan, magenta, and black. In this way, toner is supplied to each electrostatic latent image formed on each photoconductor 5 by each developing device 7, whereby the electrostatic latent image is visualized (visualized) as a toner image. .

  When the image forming operation is started, the secondary transfer backup roller 32 is driven to rotate counterclockwise in the figure, and the intermediate transfer belt 30 is caused to run in the direction indicated by the arrow in the figure. Then, a constant voltage or a constant current controlled voltage having a polarity opposite to the charging polarity of the toner is applied to each primary transfer roller 31. As a result, a transfer electric field is formed in the primary transfer nip between each primary transfer roller 31 and each photoconductor 5.

  Thereafter, when each color toner image on the photoconductor 5 reaches the primary transfer nip as each photoconductor 5 rotates, the toner image on each photoconductor 5 is formed by the transfer electric field formed in the primary transfer nip. The images are sequentially superimposed and transferred onto the intermediate transfer belt 30. Thus, a full color toner image is carried on the surface of the intermediate transfer belt 30. Further, the toner on each photoconductor 5 that could not be transferred to the intermediate transfer belt 30 is removed by the cleaning device 8. Thereafter, the surface of each photoconductor 5 is neutralized, and the surface potential is initialized.

  In the lower part of the image forming apparatus, the paper feed roller 11 starts to rotate, and the paper P is sent out from the paper feed tray 10 to the transport path R. The sheet P sent to the conveyance path R is timed by the registration roller 12 and is sent to the secondary transfer nip between the secondary transfer roller 36 and the secondary transfer backup roller 32. At this time, a transfer voltage having a polarity opposite to the toner charge polarity of the toner image on the intermediate transfer belt 30 is applied to the secondary transfer roller 36, thereby forming a transfer electric field in the secondary transfer nip.

  Thereafter, when the toner image on the intermediate transfer belt 30 reaches the secondary transfer nip as the intermediate transfer belt 30 rotates, the toner image on the intermediate transfer belt 30 is generated by the transfer electric field formed in the nip. Are collectively transferred onto the paper P. At this time, the residual toner on the intermediate transfer belt 30 that could not be transferred onto the paper P is removed by the belt cleaning device 35, and the removed toner is conveyed to a waste toner container placed in the printer body. To be recovered.

  Thereafter, the paper P is conveyed to the fixing device 20 (or 120), and the toner image on the paper P is fixed to the paper P by the fixing device 20 (or 120). Then, the paper P is discharged out of the apparatus by the paper discharge roller 13 and stocked on the paper discharge tray 14.

  The above description is an image forming operation when a full-color image is formed on a sheet. A single color image can be formed using any one of the four image forming units 4Y, 4C, 4M, and 4K. Two or three image forming units can be used to form a two-color or three-color image.

Next, the configuration of the conventional fixing device 120 will be described with reference to FIGS.
FIG. 2 is a schematic cross-sectional configuration diagram showing an embodiment of a conventional fixing device 120.
The fixing device 120 includes an endless fixing belt 121 that is a thin and flexible cylindrical fixing member, a pressure roller 122 that is a pressure member abutting from the outer peripheral side of the fixing belt 121, and the fixing belt 121. And a heat source 123 for heating. Have. As the heating source 123, for example, a halogen heater can be used, but it is not limited to this. In the example of FIG. 2, the fixing belt 121 is heated by the radiant heat of the halogen heater disposed inside (in the loop).

  A nip member 127 and a stay member 125 that fixes and supports the nip member 127 are disposed inside the fixing belt 121 in FIG. The nip member 127 forms a fixing nip portion (N shown in FIG. 2) with the pressure roller 122 via the fixing belt 121. That is, the fixing belt 121 is sandwiched between the nip member 127 and the pressure roller 122, and a fixing nip portion N is formed between the fixing belt 121 and the pressure roller 122. In the fixing nip N, the toner image on the recording material (paper) P is fixed by applying sufficient heat and pressure for fixing.

  Since the nip member 127 arranged in the width direction of the fixing belt 121 is fixedly supported by the stay member 125, the nip member 127 is prevented from being bent by the pressure from the pressure roller 122, and is pressed. A uniform nip width is obtained in the axial direction (longitudinal direction) of the roller 122. Note that the nip member 127 is preferably formed of a material having high thermal conductivity that enables heat transfer in a short time, such as copper (398 W / mk) or aluminum (236 W / mk).

  A reflecting member 128 is provided between the stay member 125 and the heating source (halogen heater) 123. By providing the reflecting member 128, the heating efficiency of the halogen heater 123 with respect to the nip member 127 is improved, and wasteful energy consumption caused by the stay member 125 being heated by the radiant heat from the halogen heater 123 can be suppressed. it can.

  Both ends of the stay member 125 and the halogen heater 123 are fixed and held by a side plate of the fixing device 120 or a separately provided holder.

  FIG. 3 is a perspective view of the fixing device shown in FIG. 2, and FIG. 4 is a view showing the positional relationship between the longitudinal ends of the members constituting the fixing device of FIG.

The nip member 127 is longer than the fixing belt 121 in the longitudinal direction, and its end is located outside the fixing belt 121. For this reason, it is possible to prevent the fixing belt 121 from being damaged by the contact of the end portion of the nip member 127.
On the other hand, the heat of the halogen heater 123 is transferred to the outside from the end of the nip member 127 and the end of the stay member 125 that similarly protrudes to the outside of the fixing belt 121, resulting in energy loss. There is a problem that it ends up.

FIG. 5 is a schematic cross-sectional configuration diagram showing an embodiment of the fixing device 20 of the present invention.
The fixing device 20 is disposed inside a rotatable endless fixing member (hereinafter also referred to as “fixing belt”) 21, a heating source 23 (23 </ b> A, 23 </ b> B) for heating the fixing member 21, and the fixing member 21. And a counter rotator (hereinafter also referred to as “pressure roller”) 22 that forms a fixing nip portion N between the nip forming unit and the nip forming unit via the fixing member 21.
Each of the fixing belt 21 and the pressure roller 22 has a shape extending longer than the width of the recording material P in a direction perpendicular to the rotation axis, that is, in a direction perpendicular to the paper surface in FIG. Can be transported by.

  The fixing belt 21 is heated by the radiant heat of a halogen heater as a plurality of heating sources 23 (23A, 23B) provided inside (in the loop). The heating source 23 is not limited to a halogen heater.

A nip forming unit is disposed inside the fixing belt 21.
The nip forming unit has at least a nip member 27 that is in contact with the inner peripheral surface of the fixing belt 21, does not change in thickness when pressed by the pressure roller 22, and performs heat transfer, and further includes the fixing belt 21 of the nip member 27. A base member 24 and a stay member 25 that reinforces the base member 24 are provided on the surface opposite to the contact surface.
The base member 24 disposed across the width direction of the fixing belt 21 is fixedly supported by the stay member 25, thereby preventing the base member 24 from being bent due to the pressure from the pressure roller 22 and applying pressure. A uniform nip width is obtained in the axial direction (longitudinal direction) of the roller 22.

The base member 24 is a heat-resistant member having a high mechanical strength and a heat-resistant temperature of 200 ° C. or more, particularly a heat-resistant resin, for example, a polyimide (PI) resin, a polyether ether ketone (PEEK) resin, and those reinforced with glass fibers. Preferably, it is configured. As a result, the deformation of the base member 24 due to heat is prevented in the toner fixing temperature region, and a stable state of the fixing nip portion N is ensured, and the output image quality is stabilized.
The stay member 25 and the halogen heaters 23A and 23B are fixedly held at both ends in the longitudinal direction by a side plate of the fixing device 20 or a separately provided holder.

An example of the nip forming unit is shown in FIG. 6A is an exploded perspective view of the nip forming unit, and FIGS. 6B and 6C are perspective views of the base member.
The nip member 27 is provided so as to cover the base member 24 and has a heat equalizing function that facilitates heat transfer in the longitudinal direction of the fixing belt 21. When the recording material P having a small size is passed, heat is prevented from staying in the end region of the fixing belt 21, and the heat is positively moved in the width direction of the fixing belt 21, that is, in the longitudinal direction of the nip member 27. , To eliminate the temperature non-uniformity in the longitudinal direction. Therefore, the nip member 27 is preferably made of a material having high thermal conductivity that enables heat transfer in a short time, such as copper (398 W / mk) or aluminum (236 W / mk).

By improving the mechanical strength of the base member 24, the nip member 27 can be made thin, and the soaking function can be improved.
Further, the base member 24 may have a structure in which a non-contact region with the nip member 27 as shown in FIGS. 6B and 6C is provided in order to reduce heat transfer to the nip member 27.

  In the example shown in FIG. 5, the facing surface where the nip member 27 and the inner peripheral surface of the fixing belt 21 are in direct contact is a nip forming surface, and the nip forming surface is flat. The nip forming surface is not limited to a flat shape, and may be a concave shape or other shapes. If the nip forming surface is concave, the discharge direction at the front end of the recording material P is closer to the pressure roller 22, so that the separability is improved and the occurrence of jam is suppressed.

  Further, in order to improve the slidability with the inner peripheral surface of the fixing belt 21, for example, a resin material having high slidability can be applied to the surface of the nip member 27 with a thickness of about 10 to 70 μm. .

  Furthermore, in order to prevent the fixing belt 21 from breaking with time, it is preferable to set the surface smoothness (surface roughness) of the nip member 27 appropriately, and between the nip member 27 and the inner peripheral surface of the fixing belt 21. The value of the coefficient of dynamic friction (μ ′) is preferably 0.20 or less. The value of the dynamic friction coefficient (μ ′) is preferably set to be 0.13 to 0.14 or less, and more preferably about 0.10. Accordingly, it is possible to prevent the fixing belt 21 from being damaged over time, and it is possible to provide a fixing device having a long life and high energy savings.

As shown in FIG. 5, a temperature sensor 29 that detects the belt temperature is provided at an appropriate position on the outer peripheral side of the fixing belt 21, for example, upstream of the fixing nip portion N in the belt rotation direction.
A separation member 40 that separates the recording material P from the fixing belt 21 is provided on the downstream side of the fixing device 20 in the conveyance direction of the recording material P.

The fixing belt 21 is an endless member that is thin and has a small diameter, such as a film, in order to reduce the heat capacity. The fixing belt 21 is an inner peripheral base formed of a metal material such as nickel or SUS or a resin material such as polyimide. And a release layer on the outer peripheral side made of PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer) or PTFE (polytetrafluoroethylene).
An elastic layer formed of a rubber material such as silicone rubber, foamable silicone rubber, or fluorine rubber may be interposed between the base material and the release layer. By setting the thickness of the elastic layer to about 100 μm, when the unfixed toner is crushed and fixed, minute irregularities on the belt surface can be absorbed by the elastic deformation of the elastic layer, and the occurrence of uneven gloss can be avoided.

The thicknesses of the base material, the elastic layer, and the release layer constituting the fixing belt 21 are preferably in the range of 20 to 50 μm, 100 to 300 μm, and 10 to 50 μm.
From the viewpoint of reducing the heat capacity, the fixing belt 21 preferably has an overall thickness of 1 mm or less and a diameter of 20 to 40 mm.
In order to further reduce the heat capacity, the thickness of the entire fixing belt 21 is preferably 0.2 mm or less, and more preferably 0.16 mm or less. The diameter is preferably 30 mm or less.

The stay member 25 is a member having a T-shaped cross section, and has an upstanding portion 25 a on the surface opposite to the fixing nip portion N. As shown in FIG. 5, the halogen heaters 23A and 23B as the main heating sources are arranged so as to be separated by the standing portion 25a.
One of the halogen heaters 23 </ b> A and 23 </ b> B has a heat generating portion at the center in the longitudinal direction corresponding to the small size recording material P, and the other has a heat generating portion at both longitudinal ends corresponding to the large size recording material P. It is what has.

  The halogen heaters 23A and 23B are configured to generate heat under output control by a power supply unit provided in the printer main body. The output control is performed based on the temperature detection result of the belt surface by the temperature sensor 29 provided on the outer periphery of the fixing belt 21. By such heater output control, the temperature of the fixing belt 21 (fixing temperature) can be set to a desired temperature.

Reflecting members 28A and 28B are provided between the stay member 25 and the halogen heaters 23A and 23B. The reflection members 28A and 28B improve the heating efficiency of the halogen heaters 23A and 23B with respect to the fixing belt 21 and suppress wasteful energy consumption due to the stay member 25 being heated by the radiant heat from the halogen heaters 23A and 23B. Can do.
The same effect can be obtained by performing heat insulation or mirror treatment on the surface of the stay member 25 instead of providing the reflecting members 28A and 28B.

The pressure roller 22 includes a cored bar, an elastic layer made of foamable silicone rubber or fluororubber provided on the surface of the cored bar, and a release layer made of PFA, PTFE, etc. provided on the surface of the elastic layer. Composed.
The pressure roller 22 is pressed by a pressing unit such as a spring and is brought into pressure contact with the fixing belt 21. The elastic layer of the pressure roller 22 is crushed at a portion that is in pressure contact with the fixing belt 21 to form a fixing nip portion N having a predetermined width. The pressurizing means is preferably a means capable of pressurization and release of pressurization.

  The pressure roller 22 is rotationally driven by a driving source such as a motor provided in the printer main body. When the pressure roller 22 is rotationally driven, the driving force is transmitted to the fixing belt 21 at the fixing nip portion N, and the fixing belt 21 is driven to rotate. The fixing belt 21 is sandwiched and rotated at the fixing nip portion N, and travels by being guided by side plate flanges disposed at both ends except for the fixing nip portion N.

  In the fixing device of the present embodiment, the pressure roller 22 is a solid roller, but may be a hollow roller. When the pressure roller 22 is a hollow roller, a heat source such as a halogen heater may be disposed inside. The elastic layer may be solid rubber, but if there is no heat source inside the pressure roller, sponge rubber may be used. Sponge rubber is more preferable because heat insulation is enhanced and heat of the fixing belt 21 is less likely to be taken away.

FIG. 7 is a perspective view showing a state in which the constituent members of the nip forming unit shown in FIG. The nip forming unit includes the base member 24, the stay member 25, and the nip member 27 as described above.
In the nip forming unit, the surface of the base member 24 opposite to the fixing nip portion N side is integrated with the flat surface of the stay member 25 on the fixing nip portion N side. The base member 24 and the stay member 25 may be formed with concavo-convex shapes such as bosses and pins on their respective surfaces, and these may be fitted in a shape-constrained manner.
The nip member 27 is fitted and integrated so as to cover a surface of the substantially rectangular parallelepiped base member 24 facing the inner peripheral surface of the fixing belt 21. Integration of the nip member 27 and the base member 24 may be performed by providing engaging members (for example, claws or the like) and engaging them, or by adhesion.

  The surface of the nip member 27 that faces the inner peripheral surface of the fixing belt 21 is a belt sliding contact surface 27a. From the viewpoint of mechanical strength, the surface that is substantially the nip forming surface is the surface facing the pressure roller 22 of the base member 24.

  The configuration of the fixing device of this embodiment will be described with reference to FIG. FIG. 8 shows a comparative example. 8 (a) and 9 (a) are side views in the longitudinal direction, and FIGS. 8 (b) and 9 (b) are partially enlarged views at the end in the longitudinal direction, as shown in FIG. The relationship between the AA cross section of the nip forming unit, the fixing belt 21 and the pressure roller 22 is shown.

8A is different from the present embodiment in that the length of the pressure roller 22 in the longitudinal direction is longer than that of the nip member 27 and the pressure roller 22 is located outside the region facing the nip member 27. Has been placed.
Since the pressure roller 22 is provided with an elastic layer made of foamable silicone rubber, fluorine rubber, or the like on the surface of the core metal, when the fixing belt 21 is strongly pressed toward the nip member 27, FIG. As shown, the inner peripheral surface of the fixing belt 21 is strongly pressed against the end portion of the nip member 27 (particularly, the abutting portion indicated by X). If the rotating and rubbing state continues in this state, the fixing belt 21 is damaged or broken starting from the vicinity of X.

On the other hand, in FIG. 9A which is the fixing device of this embodiment, the length of the pressure roller 22 in the longitudinal direction is shorter than the nip member 27, and the pressure roller 22 is disposed in a region facing the nip member 27. Has been.
In this case, the pressure roller 22 does not press the fixing belt 21 strongly against the end of the nip member 27. Further, since the thickness of the nip member 27 according to the present embodiment does not change due to the pressing of the pressure roller, the end portion does not come into strong contact with the inner peripheral surface of the fixing belt 21. That is, as shown in FIG. 9B, the inner peripheral surface of the fixing belt 21 is not in contact with the end of the nip member 27 (particularly, the portion indicated by Y) or is in a light contact state without being pressurized. Since it rotates, there is no damage or breakage with time due to rubbing.

In the configuration shown in FIG. 9, that is, in the fixing nip forming portion N, the length (width) of the pressure roller 22 in the longitudinal direction is made shorter (narrower) than the length (width) of the nip member 27 in the longitudinal direction. Further, the pressure roller 22 is disposed in the opposed region so as not to straddle the end portion of the nip member 27, so that the end portion in the longitudinal direction of the nip member 27 rubs against the inner peripheral surface of the fixing belt 21. It is possible to prevent the fixing belt 21 from being damaged or broken.
In order to prevent breakage with time, it is preferable to set the surface smoothness (surface roughness) of the nip member 27 appropriately. The value of the coefficient of dynamic friction (μ ′) between the nip member 27 and the inner peripheral surface of the fixing belt 21 is preferably about 0.10.

Next, the relationship between the lengths of the fixing belt 21 and the nip member 27 in the longitudinal direction will be described.
When the end of the nip member 127 is extended to the outside of the end of the fixing belt 121 as in the example of the conventional fixing device 120 shown in FIGS. 2 to 4, the portion other than the fixing nip portion N from the end of the nip member 127. Heat is transferred to the body and energy loss occurs.
In order to prevent this, in the configuration of the present embodiment shown in FIG. 9, the nip member 27 has a length in the longitudinal direction shorter than that of the fixing belt 21, and the inner peripheral surface of the fixing belt 21 is connected to the nip member 27. It is preferable to have the area | region which does not contact | abut at both ends.

  Further, in this embodiment, since the base member 24 has mechanical strength, the nip member 27 can be made thinner than the conventional example, and the soaking function can be improved.

FIG. 10 shows a partially enlarged view of the end portion in the longitudinal direction, similarly to FIG. 9B, for another embodiment.
In the present embodiment, the thickness of the end region in the longitudinal direction of the nip member 27 is gradually reduced from the center side toward the end side. By adopting such an end portion shape, contact between the end portion of the nip member 27 and the inner peripheral surface of the fixing belt 21 can be prevented, and damage or breakage due to rubbing can be more reliably prevented. be able to.

FIG. 11 shows a partially enlarged view of the end portion in the longitudinal direction of another embodiment.
In the present embodiment, in the end region where the fixing belt 21 is not in contact with the pressure roller 22, the surface facing the pressure roller 22 is inclined in the direction approaching the pressure roller 22, and the inner peripheral surface is the nip. It is separated from the end of the member 27.

Such a configuration can be realized by providing a support member (flange) 44 that supports the fixing belt 21.
That is, in the aspect including the support member 44 that supports the fixing belt 21 at both ends in the longitudinal direction, the support member 44 faces the pressure roller 22 in a region where the fixing belt 21 is not in contact with the pressure roller 22. The fixing belt 21 is supported such that the surface forms an inclination toward the pressure roller 22 and the inner peripheral surface is separated from the end of the nip member 27.
With such a configuration, the inner peripheral surface of the fixing belt 21 can be separated from the nip member 27, and the fixing belt 21 can be prevented from being damaged or broken by rubbing.

  Note that if the pressure contact between the fixing belt 21 and the pressure roller 22 is excessive, the fixing belt 21 may be damaged over time. Therefore, the amount of movement of the end of the fixing belt 21 toward the pressure roller 22 in the direction of the rotation axis is preferably 5% or less of the diameter of the fixing belt 21.

  The image forming apparatus provided with the above-described fixing device according to the present invention is not limited to the color laser printer shown in FIG. 1, but is mounted on a monochrome laser printer, other printers, copiers, facsimiles, or a complex machine thereof. It is possible. By mounting the fixing device of the present invention, it is possible to provide an image forming apparatus having a long life and high energy saving performance.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Bottle accommodating part 2C, 2K, 2M, 2Y Toner bottle 3 Transfer apparatus 4C, 4K, 4M, 4Y Image forming part 5 Photoconductor 6 Charging apparatus 7 Developing apparatus 8 Cleaning apparatus 9 Exposure apparatus 10 Paper feed tray 11 Paper feed roller 12 Registration roller 13 Paper discharge roller 14 Paper discharge tray 20, 120 Fixing device 21, 121 Fixing member (fixing belt)
22, 122 Opposing rotating body (pressure roller)
22a, 122a Core metal 23A, 23B, 123 Heat source (halogen heater)
24, 124 Base member 25, 125 Stay member 26 Sliding sheet 27, 127 Nip member 28A, 28B, 128 Reflecting member 29 Temperature sensor 30 Intermediate transfer belt 31 Primary transfer roller 32 Secondary transfer backup roller 33 Cleaning backup roller 34 Tension roller 35 Belt cleaning device 36 Secondary transfer roller 40 Separating member 44 Support member (flange)
N Fixing nip P Recording material (paper)

JP 2004-286922 A Japanese Patent No. 2861280 JP 2007-334205 A Japanese Patent No. 5928783 JP 2017-32770 A

Claims (7)

A rotatable endless fixing member;
A heating source for heating the fixing member;
A nip forming unit disposed inside the fixing member;
An opposing rotating body that forms a fixing nip portion with the nip forming unit via the fixing member,
The nip forming unit has at least a nip member that is in contact with an inner peripheral surface of the fixing member, does not change in thickness due to pressing of the counter rotating body, and performs heat transfer.
The fixing device according to claim 1, wherein the counter rotating body has a length in a longitudinal direction shorter than that of the nip member and is disposed in a region facing the nip member. The nip member is shorter in the longitudinal direction than the fixing member,
The fixing device according to claim 1, wherein the inner peripheral surface of the fixing member has regions at both ends that do not contact the nip member.   The nip forming unit further includes a base member and a stay member that reinforces the base member on a surface of the nip member opposite to a contact surface with the fixing member. 3. The fixing device according to 2.   4. The fixing device according to claim 1, wherein the end region in the longitudinal direction of the nip member has a shape in which the thickness gradually decreases from the center side toward the end side. 5.   In the end region where the fixing member does not come into contact with the counter rotator, the surface facing the counter rotator is inclined in a direction approaching the counter rotator, and the inner peripheral surface is separated from the end of the nip member. The fixing device according to claim 1, wherein the fixing device is provided. A support member for supporting the fixing member at both ends in the longitudinal direction;
The support member forms an inclination in a direction in which a surface of the fixing member facing the counter rotator is close to the counter rotator in an area where the support member is not in contact with the counter rotator. The fixing device according to claim 1, wherein the fixing member is supported so that a peripheral surface thereof is separated from an end portion of the nip member.   An image forming apparatus comprising the fixing device according to claim 1.